The present invention relates to electric switchgear having a pull-out frame and a switching device that can be inserted into the pull-out frame. The switching device comprises an actuating device that can be latched and serves for actuating its contact arrangement; the pull-out frame is further equipped with a positioning drive which can be coupled to the switching device and has a threaded spindle for moving the switching device.
Such switchgear has become known, for instance, through U.S. Pat. No. 4,112,269. The pull-out frame and its positioning drive are customarily designed there so that the switching device can assume three positions, namely, an operating position in which connecting leads of the switching device are in engagement with a stationary break contact device; a test position in which the connecting leads of the switching device are pulled out of the break contact arrangement but all auxiliary lines of the switching device are connected to the stationary part of the switchgear; as well as a disconnect position, in which all electrical connections between the switching device and the pull-out frame are interrupted. The transition from the operating position to the test position may pose a considerable danger for the operator and the switchgear if the switching device is closed and a load current is flowing. More or less heavy arcing can then come about between the connecting leads of the switching device and the break contact arrangement. Basically, it presents no difficulties to ensure the tripping of the switching device before its connecting leads are separated from the break contact arrangement by electrical means; for instance, the shifting of the switching device can be determined by a sufficiently sensitive probing switch and be used for actuating a working-current tripping device of the switching device. This, however, assumes that the power supply of the working current tripping device is completely undisturbed and is always ready for operation.